The present invention relates to a coolant circulation system employed in, for example, air conditioning equipment, and, in particular, to a coolant circulation system in which there is provided a refrigerating machine or a refrigerating/heating machine for regulating the temperature of a coolant.
Heretofore, a so-called constant-flow system has been commonly employed. In such a system, the output of the system is controlled in response to a change in the load imposed on the system in such a manner that the output of the refrigerating machine or refrigerating/heating machine of the system is regulated, while the coolant flow is kept constant.
Thus, in the system, even though the heat consumption of the refrigerating/heating machine can be reduced, the amount of power consumed in driving a coolant circulating pump remains unchanged. With a view to reducing the power consumption of the pump, there have been proposed various flow-rate control methods which are designed to control the output of a coolant circulation pump. Following are some examples of such proposed methods.
1) A Method Wherein Flow-rate Control is Performed on the Basis of a Detected Differential Pressure Between Coolant Headers:
This method will be described below with reference to FIG. 4 illustrating a conventional coolant circulation system.
The coolant circulation system comprises a coolant circuit and an absorption refrigerating machine. The absorption refrigerating machine includes an evaporator 1, a regenerator 2, a heat supply pipe 3 for supplying a heat to the regenerator 2, a heat supply control valve 4 and a heat supply control 5. The coolant circuit includes a coolant circulation pipe 6, a portion of which passes through the evaporator 1 to chill the coolant, a coolant outlet temperature detector 7, a supply header 8, a return header 9, a flow-rate control pump 10 for circulating coolant, a pump flow-rate control 11, a differential pressure detector 12, an air conditioner (air heat exchanger) 13, and a coolant flow rate control valve (two-way valve) 14.
In the conventional system, the coolant outlet temperature detector 7 detects a temperature of a coolant (referred to as xe2x80x9ccoolant outlet temperaturexe2x80x9d hereinbelow), as it exits the evaporator 1 where it has been chilled, and transmits a signal indicating the detected temperature to the heat supply control 5. Dependent on the transmitted signal, the heat supply control valve 4 is caused to either open or close to thereby control a heat supply to the regenerator 2, whereby output control is performed for the refrigerating machine.
In the above-described operation, when a refrigeration load is reduced, the coolant flow rate is also reduced by the air conditioner coolant flow rate control valve (two-way valve) 14 in order to save the power consumption of the coolant pump. However, at this point in the operation, there is a tendency for the differential pressure between the supply header 8 and the return header 9 to increase in excess of that which is required. For this reason, the differential pressure is detected by means of the differential pressure detector 12, and the detected differential pressure signal is transmitted to the pump flow-rate control mechanism 11 to control the flow-rate-control pump 10 in order to maintain an optimum constant differential pressure at all times.
However, it is to be noted that in the above-described method disadvantages arise as follows:
{circle around (1)} The differential pressure detector is costly.
{circle around (2)} Because the differential pressure is subject to rapid or frequent variations, it is difficult to perform effective control.
{circle around (3)} When the coolant flow rate is controlled, variations in the coolant outlet temperature become greater than in a case where such control is not performed. Consequently, significant influence is exerted on the control of the output of the refrigerating machine. Consequently, it is likely that the refrigeration operation will tend towards instability.
{circle around (4)} As a result of {circle around (3)}, the coolant outlet temperature is likely to become excessively low. Accordingly, there is a danger of the coolant freezing.
{circle around (5)} When a cooling load is dramatically reduced, the flow rate of coolant is also reduced dramatically by operation of the flow-rate control valve 14. Consequently, functioning of the refrigerating machine is liable to cease due to a reduction or suspension of coolant supply.
2) A Method Wherein Control is Performed on the Basis of a Detected Difference Between the Coolant Outlet and Inlet Temperatures:
This method will be described below with reference to the coolant circulation system shown in FIG. 5.
In FIG. 5, reference numerals 1 to 11, 13 and 14 denote the same constituent elements as those shown in FIG. 4. Reference numeral 15 denotes a coolant outlet-inlet temperature difference detector. Rather than controlling the flow-rate control pump 10 so as to maintain an optimum differential pressure between the supply header 8 and the return header 9 as is the case in the system shown in FIG. 4, in the system shown in FIG. 5 a difference between the coolant outlet and inlet temperatures is detected by means of the coolant outlet-inlet temperature difference detector 15 which transmits a signal indicating a detected temperature difference to the pump flow-rate control 11 which functions to control the variable displacement pump 10, whereby the coolant flow-rate is varied in order to maintain the temperature difference constant.
However, since in this method the coolant outlet temperature functions to influence both refrigeration output control and coolant flow-rate control, following disadvantages are encountered:
{circle around (1)} Control of refrigeration output and control of coolant flow-rate are interdependent, with the result that the system is likely to become unstable.
{circle around (2)} Overall control of the system is liable to be inaccurate since two different types of control are performed on the basis of a single factor, i.e. the coolant outlet temperature.
{circle around (3)} As a result of {circle around (2)}, the coolant outlet temperature may be reduced to such an extent that the coolant freezes.
3) A Method Wherein the Coolant Flow Rate is Varied on the Basis of the Condition of a Refrigerator Output Controller:
In this method the coolant flow rate is controlled in proportion to the degree of opening of a heat supply control valve in an absorption refrigerating machine, for example. The heat supply control valve is controlled generally on the basis of the detected coolant outlet temperature. When the coolant outlet temperature falls, the degree of opening of the heat supply control valve is reduced and, at the same time, the coolant flow rate is reduced. However, since the refrigeration output does not change rapidly, there is a danger that the temperature of the coolant will continue to fall to such an extent that the coolant freezes.
Although the foregoing method has been described with regard to a case where control is performed on the basis of the coolant outlet temperature of the refrigerating machine, a method also exists in which a heat supply control valve is controlled on the basis of a detected coolant inlet temperature. However, this method is also not reliable and there remains a danger of the coolant freezing due to fluctuations in the coolant inlet temperature.
In view of the disadvantages of the above-described conventional control methods, an object of the present invention is to provide a control method for a refrigerating or refrigerating/heating machine by which the control of a coolant circulating pump can be performed smoothly.
According to the present invention, there is provided a method for controlling a coolant circulation system including a coolant circuit and a refrigerating or refrigerating/heating machine in which a portion of the coolant circuit passes through the refrigerating or refrigerating/heating machine and includes a coolant inlet and a coolant outlet provided at opposite ends thereof, with the output of the refrigerating or refrigerating/heating machine being controlled on the basis of a temperature of the coolant at either one of the coolant inlet or the coolant outlet of the coolant circuit, the method comprising controlling a flow rate of coolant flowing in the coolant circuit on the basis of a coolant temperature at the coolant inlet.
The output of the refrigerating or refrigerating/heating machine may be controlled on the basis of a temperature of coolant at the coolant outlet.
Further, the output of the refrigerating or refrigerating/heating machine may be controlled so that the temperature of coolant at the coolant outlet is maintained substantially constant, and during an intermediate-high cooling load operation, the flow rate of coolant is controlled so that the temperature of coolant at the coolant inlet is maintained substantially constant, whereas during a low cooling load operation, the flow rate of coolant is controlled to be maintained at a predetermined value.
In accordance with an embodiment, the coolant circuit passes through a heat exchanger. In the embodiment, the method comprises detecting a difference between pressures of the coolant at positions upstream and downstream of the heat exchanger, and canceling the control of the flow rate of coolant on the basis of the coolant temperature at the coolant inlet upon detection of a predetermined value of the pressure difference.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.